The present invention relates to encasing or embedding of hard metal (that is, cemented carbides) and weldable steel in cast alloys, preferably cast iron, and to products manufactured in this way. Such products may include wear elements used in machine parts, tools, etc., that are subjected to considerable wear. Construction elements used under wear conditions and cutting bodies for cutting or working of material, e.g., cutting tips in rock drilling, are other applications.
All these products are characterized in that the parts exposed to wear or other kinds of destruction are made of cemented carbide or other hard particles in the form of lumps, crushed pieces, powder, pressed and/or sintered bodies or parts of arbitrary form embedded in a base of cast iron.
As wear elements often are parts of machines or constructions of considerable size, e.g., mining machines and the like, these elements often have to be mounted on a steel base part directly in the work place. Sometimes mechanical joints between the wear element and the steel base part can be used but such joints have a substantial risk of loosening and thus breaking down. Welding of the wear element to the steel base part is therefore preferred.
It is previously known to cast a portion of a wear part onto a preformed portion of the same composition whether steel on steel or light metal alloy onto light metal alloy. See German Pat. No. 714 013. While such construction may achieve a metallurgical bond between the portions, use of wear parts in machine construction, particularly of considerable size, results in stresses which can exceed the strength of such a metallurgical bond. In addition, such a construction requires the use of relatively expensive cast alloys for the body when such alloys are used for wear portion (as is generally the case).
It is previously known that encasing or embedding of hard metal in graphitic cast iron, a relatively inexpensive metal alloy, results in products with very high wear resistance and abrasion resistance combined with excellent strength and toughness. However, wear parts of such a composite material have poor weldability. The strength of a welded joint between graphitic cast iron and steel is relatively low and in operation the construction is sensitive to microcracks. Furthermore, direct welding of a graphitic cast iron and a constructional element of steel is very time consuming and expensive because the welding procedure requires, among other steps, preheating, well adjusted cooling, expensive special electrodes and subsequent heat treatment to obtain a satisfactory strength of the welded joint. In practice, when the welding operations have to be carried out on huge construction machines in a work place, several of these demands cannot be fulfilled.